technique of paradigm importance to elucidate the mode of action of ZnO NPs on

Gram-negative E. coli.

In addition to this, they further utilized genome-wide toxico-genomic approach

on a comprehensive level to draw a comparison between the molecular response

profiles of ZnO NPs and free Zn ions. The outcomes of the study indicated a wide-

scale alteration in the bacterial genome, thus hindering the expression of ~387 genes.

Apart from this, a significant inhibition in translation, gene expression, and RNA

modification along with a demarcating alteration in the structural physiology of

ribosomes was observed (Cui et al. 2012).

The normal physiological processes such as metabolism generally maintain the

growth and multiplication of bacteria. A slight alteration in the metabolic processes

can induce a high level of damage to the membrane and cell wall components of the

bacteria. This produces a state of oxidative stress in bacteria and ultimately leads to

cell lysis/apoptosis (Wang et al. 2017). It is not so that these metabolomic cycles take

place individually in an isolated manner; rather, they formulate an integral part of the

diverse activities taking place in a living cell. It is by virtue of this property that

metabolic alterations can be used as a viable alternative to inhibit and control the

growth of these deleterious microorganisms. In this context, ROS production and

metal ion dissolution are the two highly claimed key mechanisms found to be

responsible for the generation of an altered metabolomic process in bacteria

(Table 11.1).

Leung et al. in a study utilized liquid hue spectrum analysis to probe the probable

mechanism responsible for producing bactericidal effects in E. coli by MgO NPs

(Leung et al. 2014). It was observed that the interaction of NPs with the bacterium

resulted in unregulated metabolic protein expression along with the upregulated

activity of both weak thiamine ester binding and riboflavin metabolic proteins. The

study also pointed toward a significant downregulation of the essential mapping

proteins. Owing to which, a reduction in the metabolomic activity of bacterial cells

takes place, thus substantiating the hypothesis that targeting of protein by NPs can

result in changed bacterial cellular metabolic profiles (Leung et al. 2014; Wang et al.

2017).

Another study reported an inhibition in the expression of a model de-nitrifier

protein present in P. denitrificans by CuO NPs (Su et al. 2015b). An increase in the

concentration of CuO NPs from 0.05 to 0.25 mg/L resulted in a diminished nitrogen

removal efficiency from 98.3% to 62.1%, respectively. On further evaluation, it

came to light that the facile communication of the NPs resulted in compromised

surface morphology and integrity of the bacterial cells. This alteration in the cell

membrane permeability allowed the swift translocation of these particles inside the

vicinity of the bacterial cells. Proteomic analysis in concordance with the bioinfor-

matics analysis further revealed unregulated expression and suppression of proteins

responsible for carrying out nitrogen metabolism, electron (viz., NADH dehydroge-

nase and cytochrome), and substance (viz., GtsB (glucose transport)) transport.

Catalytic potential and expression of nitrate and nitrite reductase enzymes were

suppressed by the activity of nanoparticles (Su et al. 2015b).

11

Nanoparticles: A Potential Breakthrough in Counteracting. . .

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